﻿using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ReprojectWebMercator.Modules.glslNoise
{
    internal class glslNoise2d: GLSLFuncBase
    {
        vec3 mod289(vec3 x)
        {
            return x - floor(x * (1.0 / 289.0)) * 289.0;
        }

        vec2 mod289(vec2 x)
        {
            return x - floor(x * (1.0 / 289.0)) * 289.0;
        }

        vec3 permute(vec3 x)
        {
            return mod289(((x * 34.0) + 1.0) * x);
        }

        public float snoise(vec2 v)
        {
             vec4 C = vec4(0.211324865405187,  // (3.0-sqrt(3.0))/6.0
                                0.366025403784439,  // 0.5*(sqrt(3.0)-1.0)
                               -0.577350269189626,  // -1.0 + 2.0 * C.x
                                0.024390243902439); // 1.0 / 41.0
                                                    // First corner
            vec2 i = floor(v + dot(v, C.yy));
            vec2 x0 = v - i + dot(i, C.xx);

            // Other corners
            vec2 i1;
            //i1.x = step( x0.y, x0.x ); // x0.x > x0.y ? 1.0 : 0.0
            //i1.y = 1.0 - i1.x;
            i1 = (x0.x > x0.y) ? vec2(1.0, 0.0) : vec2(0.0, 1.0);
            // x0 = x0 - 0.0 + 0.0 * C.xx ;
            // x1 = x0 - i1 + 1.0 * C.xx ;
            // x2 = x0 - 1.0 + 2.0 * C.xx ;
            vec4 x12 = x0.xyxy + C.xxzz;
            x12.xy -= i1;

            // Permutations
            i = mod289(i); // Avoid truncation effects in permutation
            vec3 p = permute(permute(i.y + vec3(0.0, i1.y, 1.0))
              + i.x + vec3(0.0, i1.x, 1.0));

            vec3 m = max(0.5 - vec3(dot(x0, x0), dot(x12.xy, x12.xy), dot(x12.zw, x12.zw)), 0.0);
            m = m * m;
            m = m * m;

            // Gradients: 41 points uniformly over a line, mapped onto a diamond.
            // The ring size 17*17 = 289 is close to a multiple of 41 (41*7 = 287)

            vec3 x = 2.0 * fract(p * C.www) - 1.0;
            vec3 h = abs(x) - 0.5;
            vec3 ox = floor(x + 0.5);
            vec3 a0 = x - ox;

            // Normalise gradients implicitly by scaling m
            // Approximation of: m *= inversesqrt( a0*a0 + h*h );
            m *= 1.79284291400159 - 0.85373472095314 * (a0 * a0 + h * h);

            // Compute final noise value at P
            vec3 g=new ReprojectWebMercator.vec3();
            g.x = a0.x * x0.x + h.x * x0.y;
            g.yz = a0.yz * x12.xz + h.yz * x12.yw;
            return 130.0f * dot(m, g);
        }

    }
}
